I run Rwu Burn with Kor Firewalker from the board and it's fantastic - It hoses U/R Delver and Burn variants while also having play against decks like Scapeshift and Tron as their sweepers are usually Pyroclasm or Anger of the Gods.

Is it greedy? Sure, but then again if you're running a Burn deck that's splashing for 2-3 colors you should maximize card power at the expense of initial life investment, especially when it is a card that can heavily swing a match-up in your favor.

I also run Geist of Saint Traft from the sideboard, too, so you know that's how I feel about the matter.

The frowny face is correct - February/March is the optimal time to sell Standard playables from Theros at their peak. They only will go down in price as summer roles along as everyone will begin dumping their cards as rotation looms closer.

So, you know, keep the cards you expect to play with through the rest of Standard and sell/trade the rest.